Coral disease

[pufferfish]

Does anyone know the name of that white gray rubbery matt that is growing on a lot of the hard corals in the Caribbean? It is about 5mm thick and can be peeled off corals under which they are dead. I was told in San Andres, Colombia that it was from human sewage but then I saw it off Little Corn Island, Nicaragua where there is a total of of 500 people and very little sewage.

I checked out some of the reef project web sites and couldn't find any reference to it.

Anybody else seen this stuff?

 

[CJ's]

Hi Pufferfish,
Sounds like it may be Overgrowing Mat Tunicate (Tididemnum solidum). We see quite a lot of this here in Cayman but usually in a greenish hue.

According to Paul Humann it "grows in colonies of tiny tunicates embedded in a tough, smooth leathery tunic, which resembles a coating of blue-green or lime-green candle wax. The surface is covered with numerous, pore-like incurrent siphons."

Also please beware of peeling it off: "Overgrowing Mat Tunicates often go through periods of rapid growth before dying back, and occasionally disappear completely from an affected area leaving behind exposed substrate. Peeling a colony off a coral is thought to cause further spread of the organism."

Source: Reef Coral ID by Paul Humann and Ned Deloach.

Does this sound like your pal?

CJ.

 

[pufferfish]

Thanks CJ for the description. Sounds like that might be the one as it was like a piece of leather. I have ordered that book to see the picture as I couldn't find any photo on Google.

I still wonder whether the dive shop owner's claim about this stuff growing more abundantly where there is raw human sewage is just a bit of scuba fiction or reality? Maybe the reason there is a lot on San Andres is this guy keeps peeling it off. I wonder if it is spread by the peeled piece taking up root somewhere else?

In anycase it sure looks like a problem as many hard corals were covered in the stuff and the locals said it has been spreading.

Thanks again and next time I am in San Andres I will tell them to peel no more !

 

[pufferfish]

CJ, I received that book today from Amazon and it is great with all kinds of nice photos. And yes as you thought that Overgrowing Mat Tunicate seen on page 270 is the offender.

The book says on pg. 264 that, "In recent years, the occurence of overgrowths appears to have increased in many locations around the Caribbean. This growing problem may be the result of excess nutrients, bacteria, and suspended particles carried into the sea by runoff stimulating the growth of plankton and , in turn, providing additional food for sponges and tunicates."

In other words the dive shop owner's speculation on San Andres, Colombia that the increased growth is related to increased human activity and sewage is probably accurate. What amazed me is seeing the mat around Little Corn Island, Nicaragua which has very small scale tourism and only 500 people on the island who fish for lobster. The only culprit I can think of is the likely dumping of raw human sewage into the water or watertable which allows the plankton to proliferate.

I will see what I can come up with on Google as to why the proliferation. Thanks for the positive ID!

 

[pufferfish]

Not a great deal out there on the increased sightings of Trididemnum solidum except from a study in Curacao where it increased about 700% in a decade. The few studies I could find seem to implicate 'eutrophication' which is the rapid aging of a body of water due to excessive nutritents, often from human activity. They say a common cultprit is fertilizer runoff from farms and golf courses neither of which are on two islands mentioned.
The next most common cause is partially or untreated raw sewage entering the coral reef waters and stimulating the growth of micronutrients which the tunicates flourish on.

Sounds like it is time to press for better sewage treatment in the Caribbean, but hard to ask for from poorer countries when here in a wealthy country we still dump raw sewage into our oceanic harbours.

Eutrophication

Research study

 

[CJ's]

Hi Pufferfish,

Glad to hear that's a positive ID. As usual it's us humans messing things up again.

I just keep hoping that one of these days people will start to care! I think you're quite right, you can't exactly ask a poor country to finance a sewage treatment system just so that we can get better dives when we go to visit once every 5 years!

We have to get things fixed at home before we rant to others about how to manage their ecosystems.

CJ.

 

[pufferfish]

Yes it is hard to ask poor Caribbean nations to clean up their act when we continue to dump massive amounts of raw untreated sewage into our own waters. The only strong incentive for these islands to start some sort of treatment stategy is most are 'one trick ponies' relying almost exclusively on tourism to sustain their economy. Once the reef is gone so are the diver tourists. We on the other have a much more diversified economy and don't have the incentive to clean things up. On the link below four of those five Canadian cities are ocean ports (not Dawson City) and someone can correct me if I am wrong, but all except St. John's are still dumping the city's sewage into the ocean. I think finally Victoria is to start a treatment planning project this year as well.

One must lead by example before lecturing to our southern cousins.

Canadian sewage report